1. Field of the Invention
The present invention relates to a dye transfer type thermal printing sheet which can be used for high-speed recording by electronic devices such as thermal head, electrode head and laser head.
2. Description of the Prior Art
According to dye transfer type thermal printing method, a part of a sublimable dye in a coloring material layer provided on a support is transferred to an image receiving material to record an image. The coloring material layer normally comprises a sublimable dye and a binder for binding the dye onto a support. Hitherto, as the dyes used for recording of this type there have been used ionic dyes containing color former high in sublimability and transfer textile printing dyes excellent in stability used for polyester textile.
However, transfer type thermal printing sheets containing these dyes suffer from the following problems.
(1) When ionic dyes are used, sufficient color density can be obtained, but storage stability of sheets is not satisfactory. PA1 (2) Sheets in which transfer printing textile dyes for textile printing are used are inferior in coloring power because sublimability or diffusion transferability of the dyes is low and hence, it is difficult to obtain sufficient color density by thermal energy provided by ordinary thermal head. PA1 (3) Matching in color density characteristics of three colors of cyan, magenta and yellow is inferior and not only black sufficient in middle shade and saturation density cannot be obtained, but also color reproducibility of other colors is insufficient as compared with reproducibility obtained by color printing.
In order to solve these problems, improvements as proposed in unexamined-published Japanese Patent Kokai No. 60-229794 have been made, but these are still not sufficient in weather resistance of recorded image and storage stability of transfer sheet.